U.S. patent application number 14/894151 was filed with the patent office on 2016-04-28 for air-conditioning apparatus.
This patent application is currently assigned to MITSUBISHI ELECTRIC CORPORATION. The applicant listed for this patent is MITSUBISHI ELECTRIC CORPORATION. Invention is credited to Takeshi HATOMURA, Naofumi TAKENAKA, Shinichi WAKAMOTO, Kazuya WATANABE, Koji YAMASHITA.
Application Number | 20160116202 14/894151 |
Document ID | / |
Family ID | 51988208 |
Filed Date | 2016-04-28 |
United States Patent
Application |
20160116202 |
Kind Code |
A1 |
TAKENAKA; Naofumi ; et
al. |
April 28, 2016 |
AIR-CONDITIONING APPARATUS
Abstract
An air-conditioning apparatus includes: a compressor allowing
refrigerant injection thereto and compress and discharge the
refrigerant at a high temperature; an indoor heat exchanger
exchanging heat between air and refrigerant; a first flow rate
control device adjusting and controlling a flow rate of
refrigerant; and a plurality of outdoor heat exchangers being in
parallel to exchange heat between outside air and refrigerant, a
first defrosting pipe allowing a branched part of the refrigerant
discharged from the compressor to pass and flow into the outdoor
heat exchanger to be defrosted; a reducing device adjusting a
pressure of refrigerant passing through the first defrosting pipe
to a medium pressure; a second defrosting pipe from which the
refrigerant having passed through the outdoor heat exchanger to be
defrosted is injected into the compressor; and a reducing device
adjusting a pressure of refrigerant passing through the second
defrosting pipe to an injection pressure.
Inventors: |
TAKENAKA; Naofumi;
(Chiyoda-ku, JP) ; WAKAMOTO; Shinichi;
(Chiyoda-ku, JP) ; WATANABE; Kazuya; (Chiyoda-ku,
JP) ; YAMASHITA; Koji; (Chiyoda-ku, JP) ;
HATOMURA; Takeshi; (Chiyoda-ku, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
MITSUBISHI ELECTRIC CORPORATION |
Tokyo |
|
JP |
|
|
Assignee: |
MITSUBISHI ELECTRIC
CORPORATION
Chiyoda-ku, Tokyo
JP
|
Family ID: |
51988208 |
Appl. No.: |
14/894151 |
Filed: |
May 31, 2013 |
PCT Filed: |
May 31, 2013 |
PCT NO: |
PCT/JP2013/065210 |
371 Date: |
November 25, 2015 |
Current U.S.
Class: |
62/140 |
Current CPC
Class: |
F25B 2700/2106 20130101;
F25B 2313/006 20130101; F25D 21/002 20130101; F25B 2313/0253
20130101; F25B 13/00 20130101; F25B 2313/02741 20130101; F25B
2313/0233 20130101; F25B 47/022 20130101 |
International
Class: |
F25D 21/00 20060101
F25D021/00; F25B 13/00 20060101 F25B013/00 |
Claims
1. An air-conditioning apparatus comprising: a compressor to allow
refrigerant to be injected into a portion thereof located
intermediate of a compression stroke, suck the refrigerant having a
low pressure, compress the refrigerant, and discharge the
refrigerant having a high temperature; an indoor heat exchanger to
exchange heat between air to be conditioned and the refrigerant; a
first flow rate control device to adjust and control a flow rate of
the refrigerant passing through the indoor heat exchanger; a
plurality of outdoor heat exchangers connected in parallel to
exchange heat between outdoor air and the refrigerant, the
compressor, the indoor heat exchanger, the first flow rate control
device, and the plurality of outdoor heat exchangers being
connected by pipes to form a main refrigerant circuit in which the
refrigerant circulates; a first defrosting pipe to allow a branched
part of the refrigerant discharged from the compressor to pass
therethrough and flow into at least one of the outdoor heat
exchangers to be defrosted; a first pressure adjustment device to
adjust a pressure of the refrigerant passing through the first
defrosting pipe to a medium pressure higher than the low pressure
and lower than the high pressure; a second defrosting pipe to allow
the refrigerant that has passed through the at least one of the
outdoor heat exchangers to be defrosted to pass therethrough to be
injected into the compressor; and a second pressure adjustment
device to adjust a pressure of the refrigerant passing through the
second defrosting pipe to an injection pressure.
2. The air-conditioning apparatus of claim 1, being configured to
perform defrosting and heating by causing at least one of the
outdoor heat exchangers other than the at least one of the outdoor
heat exchangers to be defrosted to serve as an evaporator.
3. The air-conditioning apparatus of claim 2, further comprising a
third pressure adjustment device to adjust a pressure of the
refrigerant that has flowed out of the at least one of the outdoor
heat exchangers to be defrosted and cause the refrigerant to flow
into upstream of the outdoor heat exchanger, serving as the
evaporator, in the main refrigerant circuit.
4. The air-conditioning apparatus of claim 3, further comprising a
refrigerant-refrigerant heat exchanger to exchange heat between the
refrigerant flowing in the main refrigerant circuit to flow into
the at least one of the outdoor heat exchangers serving as the
evaporator and the refrigerant flowing in the second defrosting
pipe.
5. The air-conditioning apparatus of claim 1, further comprising a
fourth pressure adjustment device to adjust a pressure of the
refrigerant flowing in the main refrigerant circuit and cause the
refrigerant to flow into the second defrosting pipe.
6. The air-conditioning apparatus of claim 1, wherein the outdoor
heat exchanger includes a plurality of heat transfer tubes to allow
the refrigerant to pass therethrough, the plurality of heat
transfer tubes arranged in a plurality of levels extending
perpendicularly to direction of passage of air and in a plurality
of columns extending in parallel with the direction of passage of
air, and a plurality of fins spaced from one another so that air
passes therethrough in the direction of passage of air, a pipe
connected to the heat transfer tubes in a column upstream in the
direction of passage of air is connected to the first defrosting
pipe, and a pipe connected to the heat transfer tubes in a column
downstream in the direction of passage of air is connected to the
second defrosting pipe.
7. The air-conditioning apparatus of claim 3, wherein the third
pressure adjustment device is configured to control a pressure of
the refrigerant flowing out of at least one of the outdoor heat
exchangers to be defrosted.
8. The air-conditioning apparatus of claim 7, wherein the third
pressure adjustment device is configured to control the pressure of
the refrigerant flowing out of the at least one of the outdoor heat
exchangers to be defrosted to have a pressure corresponding to a
saturation temperature of higher than 0 degrees C. and lower than
or equal to 10 degrees C.
9. The air-conditioning apparatus of claim 1, being configured to
control a discharge temperature or a discharge superheat of the
refrigerant discharged from the compressor by adjustment of
pressure by the second pressure adjustment device.
10. The air-conditioning apparatus of claim 1, further comprising
an outdoor-air temperature detector to detect an outdoor-air
temperature of air outside a space to be air-conditioned, wherein
the first pressure adjustment device is configured to perform a
flow rate control based on the outdoor-air temperature.
11. The air-conditioning apparatus of claim 1, further comprising
an outdoor-air temperature detector to detect an outdoor-air
temperature of air outside a space to be air-conditioned, the
air-conditioning apparatus being configured to change a criterion
for determining whether to start a defrosting operation, based on
the outdoor-air temperature.
12. The air-conditioning apparatus of claim 1, further comprising
an outdoor-air temperature detector to detect an outdoor-air
temperature of air outside a space to be air-conditioned, the
air-conditioning apparatus being configured to select, based on the
outdoor-air temperature, from a heating-and-defrosting operation
mode in which the at least one of the outdoor heat exchangers to be
defrosted is selected and defrosted and another one of the outdoor
heat exchangers serves as an evaporator so as to continue heating,
and a heating-stop defrosting operation mode in which all the
outdoor heat exchangers are defrosted.
13. The air-conditioning apparatus of claim 1, further comprising
an outdoor-air temperature detector to detect an outdoor-air
temperature of air outside a space to be air-conditioned, and an
outdoor fan to blow the outdoor air to the plurality of outdoor
heat exchangers, the air-conditioning apparatus being configured to
change, based on the outdoor-air temperature, output power of the
outdoor fan in defrosting the at least one of the outdoor heat
exchangers to be defrosted.
14. The air-conditioning apparatus of claim 1, being configured to
defrost each of the plurality of outdoor heat exchangers at least
once in the defrosting operation mode.
Description
TECHNICAL FIELD
[0001] The present invention relates to an air-conditioning
apparatus.
BACKGROUND ART
[0002] In view of global environmental protection, boiler-type
heating appliances for heating by burning fossil fuel have been
replaced by heat-pump-type air-conditioning apparatuses using air
as heat sources in more and more cases even in cold regions in
recent years. The heat-pump-type air-conditioning apparatus can
efficiency perform heating because heat is supplied from air in
addition to an electrical input to a compressor.
[0003] On other hand, in the heat-pump-type air-conditioning
apparatus, however, frost is more easily accumulated on an outdoor
heat exchanger serving as an evaporator as the temperature of air
in, for example, the outside (outdoor-air temperature) decreases.
Thus, it is necessary to perform defrosting (frost removal) for
melting frost on the outdoor heat exchanger. For such defrosting,
an example method is to reverse a refrigerant flow in heating so as
to supply refrigerant from a compressor to an outdoor heat
exchanger. This method, however, is performed while heating of a
room is stopped in some cases, and thus, has the problem of a loss
of comfort.
[0004] In view of this, to perform heating during defrosting,
proposed are methods for heating by dividing outdoor heat
exchangers in such a manner that while some of the outdoor heat
exchangers are defrosted, the other outdoor heat exchangers operate
as evaporators so as to absorb heat from air, for example (e.g.,
Patent Literature 1, Patent Literature 2, and Patent Literature
3).
[0005] For example, in a technique described in Patent Literature
1, an outdoor heat exchanger is divided into two heat exchanger
parts. Then, to defrost one of the heat exchanger parts, an
electronic expansion valve disposed upstream of this heat exchanger
part is closed. In addition, an electromagnetic shut-off valve of a
bypass pipe for conveying refrigerant from a discharge pipe of a
compressor to an inlet of the heat exchanger part for bypassing is
opened so that part of high-temperature refrigerant discharged from
the compressor flows directly into the heat exchanger part to be
defrosted. When defrosting of one of the heat exchanger parts is
completed, defrosting of the other heat exchanger part is
performed. In this case, in a heat exchanger part to be defrosted,
defrosting is performed in a state in which the pressure of
refrigerant in this heat exchanger part is substantially equal to a
suction pressure of the compressor (low-pressure defrosting).
[0006] In a technique described in Patent Literature 2, a plurality
of heat source units and at least one indoor unit are provided, and
refrigerant discharged from a compressor is caused to flow directly
into a heat source unit side heat exchanger to be defrosted by
reversing connection of a four-way valve of only a heat source unit
including the heat source side heat exchanger to be defrosted. In
this case, in the heat source unit side heat exchanger to be
defrosted, defrosting is performed in a state in which the pressure
of refrigerant in this heat source unit side heat exchanger is
substantially equal to a discharge pressure of the compressor
(high-pressure defrosting).
[0007] In a technique described in Patent Literature 3, an outdoor
heat exchanger is divided into a plurality of outdoor heat
exchanger parts in such a manner that part of high-temperature
refrigerant discharged from a compressor alternately flows into the
outdoor heat exchanger parts so as to alternately defrost the
outdoor heat exchanger parts. Thus, heating can be continuously
performed without reversing a refrigeration cycle. Refrigerant
supplied to an outdoor heat exchanger part to be defrosted is
injected from an injection port of the compressor. In this case, in
the outdoor heat exchanger part to be defrosted, defrosting is
performed in a state in which the pressure of refrigerant in this
outdoor heat exchanger part is lower than a discharge pressure of
the compressor and higher than a suction pressure of the compressor
(a pressure that is slightly higher than 0 degrees C. in terms of
saturation temperature) (medium-pressure defrosting).
CITATION LIST
Patent Literature
[0008] Patent Literature 1: Japanese Unexamined Patent Application
Publication No. 2009-085484 ([0019], FIG. 3)
[0009] Patent Literature 2: Japanese Unexamined Patent Application
Publication No. 2007-271094 ([0007], FIG. 2)
[0010] Patent Literature 3: International Publication No.
WO2012/014345 ([0006], FIG. 1)
SUMMARY OF INVENTION
Technical Problem
[0011] In the low-pressure defrosting described in Patent
Literature 1, a heat exchanger part to be defrosted and a heat
exchanger part serving as an evaporator (i.e., a heat exchanger
part not to be defrosted) operate in the same pressure range. In
the heat exchanger part serving as an evaporator, refrigerant takes
heat from outdoor air. Thus, an evaporating temperature of
refrigerant needs to be lower than an outdoor-air temperature. To
achieve this, in the heat exchanger part to be defrosted, a
saturation temperature of refrigerant is lower than or equal to 0
degrees C. in some cases. Accordingly, condensation latent heat of
refrigerant cannot be used for melding frost (0 degrees C.), and
the efficiency of defrosting is low in some cases.
[0012] In the high-pressure defrosting described in Patent
Literature 2, subcooling (the degree of subcooling) of refrigerant
at an outlet of a heat source side heat exchanger whose defrosting
has finished increases. Thus, temperature distribution occurs in a
heat source side heat exchanger to be defrosted, and efficient
defrosting cannot be performed. In addition, a large degree of
subcooling causes an increase in the amount of liquid refrigerant
in the heat source side heat exchanger to be defrosted, and thus,
it takes time for liquid refrigerant to move in some cases.
[0013] In the medium-pressure defrosting described in Patent
Literature 3, condensation latent heat is utilized by controlling
the saturation temperature of refrigerant in a state (about 0 to 10
degrees C.) slightly higher than zero. This medium-pressure
defrosting shows a small temperature variation of the entire
outdoor heat exchanger parts as compared to the low-pressure
defrosting and the high-pressure defrosting, and thus, defrosting
can be efficiently performed. However, the amount of liquid of
refrigerant that can be injected into the compressor is limited,
and the flow rate of refrigerant that can be supplied to the
outdoor heat exchanger part to be defrosted is limited. In
addition, the pressure of the outdoor heat exchanger part to be
defrosted might be affected by an injection pressure of an
injection compressor. Thus, defrosting capacity is limited, and the
time cannot be shortened.
[0014] The present invention has been made to solve problems as
described above, and it is therefore an object of the present
invention to provide an air-conditioning apparatus that can
efficiently perform defrosting.
Solution to Problem
[0015] An air-conditioning apparatus according to the present
invention includes: a compressor configured to allow refrigerant to
be injected into a portion located intermediate of a compression
stroke, suck refrigerant having a low pressure, compress the
refrigerant, and discharge refrigerant having a high temperature;
an indoor heat exchanger configured to exchange heat between air to
be conditioned and the refrigerant; a first flow rate control
device configured to adjust and control a flow rate of the
refrigerant passing through the indoor heat exchanger; a plurality
of outdoor heat exchangers connected in parallel and configured to
exchange heat between outdoor air and the refrigerant, the
compressor, the indoor heat exchanger, the first flow rate control
device, and the plurality of outdoor heat exchangers being
connected by pipes and forming a main refrigerant circuit in which
the refrigerant circulates; a first defrosting pipe through which a
branched part of the refrigerant discharged from the compressor
passes and flows into at least one of the outdoor heat exchangers
to be defrosted; a first pressure adjustment device configured to
adjust the refrigerant passing through the first defrosting pipe to
a medium pressure higher than the low pressure and lower than the
high pressure; a second defrosting pipe from which the refrigerant
that has passed through the at least one of the outdoor heat
exchangers to be defrosted is injected into the compressor; and a
second pressure adjustment device configured to adjust a pressure
of refrigerant passing through the second defrosting pipe to an
injection pressure.
Advantageous Effects of Invention
[0016] The present invention provides an air-conditioning apparatus
in which defrosting is performed by causing refrigerant to flow
into an outdoor heat exchanger to be defrosted through a path
different from a main refrigerant circuit under a pressure adjusted
by a first pressure adjustment device and a second pressure
adjustment device. Thus, the defrosting can be efficiently
performed without stopping heating of an indoor unit, for
example.
BRIEF DESCRIPTION OF DRAWINGS
[0017] FIG. 1 illustrates a configuration of an air-conditioning
apparatus 100 according to Embodiment 1 of the present
invention.
[0018] FIG. 2 illustrates an example configuration of an outdoor
heat exchanger of the air-conditioning apparatus 100 according to
Embodiment 1 of the present invention.
[0019] FIG. 3 is a table showing states of ON/OFF (opening/closing)
or opening degree adjustment of devices having valves in the
air-conditioning apparatus 100 according to Embodiment 1 of the
present invention.
[0020] FIG. 4 is a view showing a flow of refrigerant in a cooling
operation of the air-conditioning apparatus 100 according to
Embodiment 1 of the present invention.
[0021] FIG. 5 is a P-h diagram in the cooling operation of the
air-conditioning apparatus 100 according to Embodiment 1 of the
present invention.
[0022] FIG. 6 is a view showing a flow of refrigerant in a heating
normal operation of the air-conditioning apparatus 100 according to
Embodiment 1 of the present invention.
[0023] FIG. 7 is a P-h diagram in the heating normal operation of
the air-conditioning apparatus 100 according to Embodiment 1 of the
present invention.
[0024] FIG. 8 is a view showing a flow of refrigerant in a heating
defrosting operation of the air-conditioning apparatus 100
according to Embodiment 1 of the present invention.
[0025] FIG. 9 is a P-h diagram in the heating defrosting operation
of the air-conditioning apparatus 100 according to Embodiment 1 of
the present invention.
[0026] FIG. 10 shows a heating capacity ratio with respect to a
pressure (in terms of saturated liquid temperature) of an outdoor
heat exchanger 13 to be defrosted in the air-conditioning apparatus
100 according to Embodiment 1 of the present invention.
[0027] FIG. 11 shows an enthalpy difference between before inflow
and after outflow of refrigerant into/from an outdoor heat
exchanger 13 to be defrosted with respect to the pressure (in terms
of saturated liquid temperature) in the air-conditioning apparatus
100 according to Embodiment 1 of the present invention.
[0028] FIG. 12 shows a flow rate ratio of the outdoor heat
exchanger 13 to be defrosted with respect to the pressure (in terms
of saturated liquid temperature) in the air-conditioning apparatus
100 according to Embodiment 1 of the present invention.
[0029] FIG. 13 shows a refrigerant amount of the outdoor heat
exchanger 13 to be defrosted with respect to the pressure (in terms
of saturated liquid temperature) in the air-conditioning apparatus
100 according to Embodiment 1 of the present invention.
[0030] FIG. 14 shows a subcooling SC of refrigerant at an outlet of
the at least one of the outdoor heat exchangers to be defrosted
with respect to the pressure (in terms of saturated liquid
temperature) of the outdoor heat exchanger 13 to be defrosted in
the air-conditioning apparatus 100 according to Embodiment 1 of the
present invention.
[0031] FIG. 15 is a flowchart showing control of a control device
60 in the air-conditioning apparatus 100 according to Embodiment 1
of the present invention.
[0032] FIG. 16 illustrates a configuration of an air-conditioning
apparatus 101 according to Embodiment 2 of the present
invention.
[0033] FIG. 17 is a table showing states of ON/OFF
(opening/closing) or opening degree adjustment of devices having
valves in the air-conditioning apparatus 100 according to
Embodiment 2 of the present invention.
[0034] FIG. 18 is a view showing a flow of refrigerant in a heating
defrosting operation of the air-conditioning apparatus 101
according to Embodiment 2 of the present invention.
[0035] FIG. 19 is a P-h diagram in the heating defrosting operation
of the air-conditioning apparatus 101 according to Embodiment 2 of
the present invention.
[0036] FIG. 20 illustrates a configuration of an air-conditioning
apparatus 102 according to Embodiment 3 of the present
invention.
[0037] FIG. 21 illustrates a configuration of an air-conditioning
apparatus 103 according to Embodiment 4 of the present
invention.
[0038] FIG. 22 illustrates a configuration of an air-conditioning
apparatus 104 according to Embodiment 4 of the present
invention.
DESCRIPTION OF EMBODIMENTS
[0039] Embodiments of the present invention will be described with
reference to the drawings. In the drawings, the same reference
characters designate the same or like components, and the same
holds for the entire description of the specification. The
configurations of components in the following description are
merely examples, and the present invention is not limited to these
examples. In particular, combinations of components are not limited
to those in the embodiments, and components in one embodiment are
applicable to another embodiment. Similar devices distinguished by
suffixes, for example, may be collectively referred to without the
suffixes when these devices do not need to be individually
distinguished or specified. The levels of, for example, temperature
and pressure are not determined based on specific absolute values,
and are determined relative to the states, operation, and other
factors in, for example, a system or a device.
Embodiment 1
[0040] FIG. 1 illustrates a configuration of an air-conditioning
apparatus 100 according to Embodiment 1 of the present invention.
The air-conditioning apparatus 100 of this embodiment includes an
outdoor unit 10 and a plurality of indoor units 30a and 30b. The
outdoor unit 10 is connected to the indoor units 30a and 30b by
first extension pipes 40, 41a, and 41b and second extension pipes
50, 51a, and 51b, thereby forming a refrigerant circuit. In the
refrigerant circuit, the indoor unit 30a and the indoor unit 30b
are connected in parallel with the outdoor unit 10. The
air-conditioning apparatus 100 includes a control device 60. The
control device 60 performs a process based on, for example, a
temperature and a pressure detected by detectors (sensors) provided
in the air-conditioning apparatus 100, controls devices in the
air-conditioning apparatus 100, and controls cooling and heating of
a space to be air-conditioned performed at least one of the indoor
unit 30a or 30b. An outdoor-air temperature sensor 61 is a
temperature detector for detecting an outdoor temperature. The
air-conditioning apparatus according to this embodiment also
includes a pressure sensor and a temperature sensor for detecting a
pressure and a temperature of refrigerant discharged and sucked
from/into the compressor 11. The air-conditioning apparatus also
includes, for example, temperature sensors for detecting, for
example, temperatures of refrigerant in outdoor heat exchangers 13
and an indoor heat exchanger 31.
[0041] Examples of refrigerant circulating in a refrigerant circuit
include fluorocarbon refrigerant and HFO refrigerant. Examples of
the fluorocarbon refrigerant include a HFC-based refrigerant such
as R32 refrigerant, R125, and R134a, and a refrigerant mixture of
these refrigerants, such as R410A, R407c, or R404A. Examples of the
HFO refrigerant include HFO-1234yf, HFO-1234ze (E), and HFO-1234ze
(Z). Examples of other refrigerants include refrigerants for use in
vapor compression heat pumps, such as CO.sub.2 refrigerant, HC
refrigerant (e.g., propane or isobutane refrigerant), ammonia
refrigerant, and refrigerant mixture of R32 and HFO-1234yf.
[0042] In the air-conditioning apparatus 100 of this embodiment 1,
the two indoor units 30a and 30b are connected to one outdoor unit
10. Alternatively, only one indoor unit 30 may be provided, or
three such indoor units may be connected in parallel. Two or more
outdoor units 10 may also be connected to in parallel. In addition,
a refrigerant circuit configuration may be employed in such a
manner that cooling and heating can be simultaneously performed,
that is, each of the indoor units 30 is individually allowed to
select cooling or heating by, for example, providing a switching
valve in the indoor unit 30.
[0043] A configuration of the refrigerant circuit in the
air-conditioning apparatus 100 will now be described. The
refrigerant circuit of the air-conditioning apparatus 100 includes
a refrigerant circuit serving as a main circuit (main refrigerant
circuit) formed by connecting the compressor 11, a cooling/heating
switching device 12, and an outdoor heat exchanger 13 of the
outdoor unit 10 to an indoor heat exchanger 31 and a first flow
rate control device 32 that is freely opened and closed of the
indoor unit 30 by pipes. In this embodiment, although an
accumulator 14 is connected to the main refrigerant circuit, the
accumulator 14 is not a necessary component, and thus, may not be
connected to the main refrigerant circuit.
[0044] The compressor 11 sucks refrigerant, compresses the
refrigerant into a high-temperature high-pressure gaseous state,
and discharges the resulting refrigerant. The compressor 11 of this
embodiment includes a port that allows injection (refrigerant
introduction) into a portion located intermediate of a compression
stroke in a compression chamber (not shown). For example, a
discharge temperature can be reduced, for example, by injecting
liquid refrigerant under a predetermined pressure (injection
pressure). The compressor 11 is a compressor of a type that can
control the rotation speed (driving frequency) by using, for
example, an inverter circuit so as to change the discharge amount
(discharge capacity) of refrigerant. The cooling/heating switching
device 12 is connected to a point between a discharge pipe 22 and a
suction pipe 23 of the compressor 11 and switches the direction of
refrigerant flow. The cooling/heating switching device 12 is
constituted by, for example, a four-way valve. Based on an
instruction of the control device 60, the cooling/heating switching
device 12 switches between a pipe connection state indicated by
continuous lines in FIG. 1 in a heating operation and a pipe
connection state indicated by broken lines in FIG. 1 in a cooling
operation.
[0045] FIG. 2 illustrates an example configuration of the outdoor
heat exchanger 13 of the air-conditioning apparatus 100 according
to Embodiment 1 of the present invention. As illustrated in FIG. 2,
the outdoor heat exchanger of this embodiment is a fin-and-tube
heat exchanger including a plurality of heat transfer tubes 5a and
a plurality of fins 5b, for example. The heat transfer tubes 5a
allow refrigerant to pass therethrough and are arranged in a
plurality of levels extending perpendicularly to direction of
passage of air and a plurality of columns extending in parallel
with the direction of passage of air. The fins 5b are spaced from
one another in such a manner that air passes therethrough in the
direction of passage of air.
[0046] As illustrated in FIG. 2, for the outdoor heat exchanger 13
of this embodiment, one outdoor heat exchanger includes a plurality
of independent channels. This outdoor heat exchanger is divided
into a plurality of outdoor heat exchangers 13 by inlets and
outlets of the channels in parallel with the refrigerant main
circuit. In this example, the outdoor heat exchanger is divided
into two outdoor heat exchangers 13a and 13b. The outdoor heat
exchanger is not necessarily divided into two. The outdoor heat
exchanger may be divided into left and right exchangers (i.e.,
horizontal division). In this case, however, the inlet and outlet
of refrigerant of each of the outdoor heat exchangers 13a and 13b
are separated at the left and right ends of the outdoor unit 10,
which complicates connection of pipes. In view of this, the outdoor
heat exchanger is preferably divided into upper and lower
exchangers (i.e., vertical division) as illustrated in FIG. 2. In
addition, as illustrated in FIG. 2, the fins 5b are common to the
outdoor heat exchangers 13a and 13b of this embodiment, that is,
are not divided.
[0047] Thus, in a heating defrosting operation described later,
high-temperature refrigerant flows in the heat transfer tubes 5a
and heats the fins 5b in order to melt frost in one of the outdoor
heat exchangers 13, whereas refrigerant flowing in the heat
transfer tubes 5a takes heat through the fins 5b in the other
outdoor heat exchanger 13. In view of this, to prevent leakage of
heat between the outdoor heat exchangers 13, the fins 5b are
divided into parts individually corresponding to the outdoor heat
exchangers 13.
[0048] An outdoor fan 21 causes air in the outside (outdoor air) to
pass through the outdoor heat exchangers 13a and 13b so as to
promote heat exchange with refrigerant. In FIG. 1, one outdoor fan
21 is provided for the outdoor heat exchangers 13a and 13b, but may
be provided for each of the outdoor heat exchangers 13a and
13b.
[0049] First connection pipes 24a and 24b are connected to the
outdoor heat exchangers 13a and 13b, respectively. In this
embodiment, the connection pipes 24a and 24b are connected to the
refrigerant inflow ends of the outdoor heat exchangers 13a and 13b
in a heating operation. Second flow rate control devices 15a and
15b are provided in channels of the first connection pipes 24a and
24b, respectively. The second flow rate control devices 15a and 15b
are constituted by electronically controlled expansion valves.
Based on an instruction from the control device 60, the second flow
rate control devices 15a and 15b change the opening degrees thereof
so as to control a flow rate of refrigerant by pressure adjustment.
The second flow rate control devices 15a and 15b of Embodiment 1
correspond to a "third pressure adjustment device" of the present
invention.
[0050] Second connection pipes 25a and 25b are connected to the
outdoor heat exchangers 13a and 13b, respectively, at the opposite
ends to the first connection pipes 24a and 24b. In this embodiment,
the second connection pipes 25a and 25b are connected to
refrigerant outflow ends of the outdoor heat exchangers 13a and 13b
in the heating operation. First solenoid valves 16a and 16b are
provided in channels of the second connection pipes 25a and 25b,
respectively. Based on an instruction from the control device 60,
each of the first solenoid valves 16a and 16b switches, by opening
and closing the valve, as to whether or not refrigerant flows
into/from the outdoor heat exchangers 13a and 13b from the main
refrigerant circuit.
[0051] The air-conditioning apparatus 100 of this embodiment
further includes a first defrosting pipe 26 as a channel different
from the refrigerant main circuit. The first defrosting pipe 26 has
one end connected to the discharge pipe 22 and the other end
branched into parts respectively connected to the second connection
pipes 25a and 25b. The first defrosting pipe 26 supplies part of
high-temperature high-pressure refrigerant discharged from the
compressor 11 to at least one of the outdoor heat exchangers 13a
and 13b for defrosting. The first defrosting pipe 26 includes a
reducing device 18. Based on an instruction from the control device
60, the reducing device 18 reduces the pressure of part of the
high-temperature high-pressure refrigerant discharged from the
compressor 11 to a medium pressure. The medium pressure herein is a
pressure lower than a high pressure (discharge pressure) and higher
than an injection pressure and a low pressure (suction pressure).
Thus, in defrosting, the refrigerant whose pressure has been
reduced to the medium pressure is supplied to the outdoor heat
exchangers 13a and 13b. Second solenoid valves 17a and 17b are
provided in branched parts of the first defrosting pipe 26. Each of
the second solenoid valves 17a and 17b switches as to whether or
not refrigerant flows into the second connection pipes 25a and 25b
from the discharge pipe 22 through the first defrosting pipe 26.
The reducing device 18 corresponds to a "first pressure adjustment
device" of the present invention.
[0052] The first solenoid valves 16a and 16b and the second
solenoid valves 17a and 17b only need to switch channels between
the main refrigerant circuit and the first defrosting pipe 26.
Thus, the first solenoid valves 16a and 16b and the second solenoid
valves 17a and 17b may be constituted by four-way valves, three-way
valves, or two way valves, for example. For example, each of the
first solenoid valves 16a and 16b reverses the pressures at the
front and rear thereof because refrigerant therein flows in
different directions in different operations. A typical solenoid
valve cannot be used in some cases when the front and rear
pressures are reversed. In view of this, a four-way valve whose
high-pressure sides are connected to the discharge pipe 22 and
low-pressure sides are connected to the suction pipe 23 can be
employed so as to have the same function as the first solenoid
valves 16a and 16b. Since the sides of the second solenoid valves
17a and 17b connected to the first defrosting pipe 26 at the
discharge pipe 22 are always at high pressures, and thus, may be
two way valves each of which switches in two directions.
[0053] The reducing device 18 may be constituted by a capillary
tube as long as a necessary defrosting capacity (the flow rate of
refrigerant to flow into the first defrosting pipe 26 for
defrosting) is determined. The sizes of the second solenoid valves
17a and 17b may be reduced without using the reducing device 18 so
that the pressures thereof are reduced to a medium pressure at a
predetermined defrosting flow rate. A flow rate control device may
be provided instead of the second solenoid valves 17a and 17b,
without using the reducing device 18. In such cases, the second
solenoid valves 17a and 17b or the flow rate control device, for
example, corresponds to a "first pressure adjustment device" of the
present invention.
[0054] The second defrosting pipe 27 also serve as a channel
different from the refrigerant main circuit. The second defrosting
pipe 27 has one end connected to a port at an injection portion of
the compressor 11 and the other end branched into parts
respectively connected to the first connection pipes 24a and 24b.
The second defrosting pipe 27 includes a reducing device 20 and
third solenoid valves 19a and 19b. In a heating defrosting
operation described later, the reducing device 20 reduces the
pressure of part of medium-temperature medium-pressure refrigerant
that has flowed from the outdoor heat exchanger 13a or 13b to an
injection pressure. The refrigerant whose pressure has been reduced
is injected into the compressor 11. Each of the third solenoid
valves 19a and 19b is provided at a branch point in the second
defrosting pipe 27, and switches as to whether or not refrigerant
flows from the first connection pipes 24a and 24b to the second
defrosting pipe 27. The reducing device 20 corresponds to a "second
pressure adjustment device" of the present invention.
[0055] Operational behaviors of operations performed by the
air-conditioning apparatus 100 of this embodiment will now be
described. The operations performed by the air-conditioning
apparatus 100 include two operations: a cooling operation and a
heating operation. The heating operation includes a heating normal
operation and a heating defrosting operation (also referred to as a
continuous heating operation). In the heating normal operation,
both the outdoor heat exchangers 13a and 13b constituting the
outdoor heat exchangers 13 operate as evaporators. The heating
defrosting operation is an operation in which the outdoor heat
exchanger 13a and the outdoor heat exchanger 13b are alternately
defrosted while a heating operation continues. Specifically, a
heating operation is performed with one of the outdoor heat
exchangers 13 operating as an evaporator, whereas the other outdoor
heat exchanger 13 is defrosted. When the defrosting of the latter
outdoor heat exchanger 13 is finished, this outdoor heat exchanger
then operates as an evaporator to perform a heating operation,
whereas the former outdoor heat exchanger 13 is defrosted.
[0056] FIG. 3 is a table showing states of ON/OFF (opening/closing)
or opening degree adjustment of devices (valves) having valves in
operations of the air-conditioning apparatus 100 according to
Embodiment 1 of the present invention. In FIG. 3, with regard to
the cooling/heating switching device 12, ON represents a connection
state indicated by the continuous lines in FIG. 1, whereas OFF
represents a connection state indicated by the broken lines in FIG.
1. With regard to each of the solenoid valves 16a, 16b, 17a, 17b,
19a, and 19b, ON represents a state in which the valve is open so
that refrigerant flows, whereas OFF represents a state in which the
valve is closed so that refrigerant does not flow.
[Cooling Operation]
[0057] FIG. 4 is a view showing a flow of refrigerant in a cooling
operation of the air-conditioning apparatus 100 according to
Embodiment 1 of the present invention. In FIG. 4, bold lines
represent sections where refrigerant flows in the cooling
operation, and thin lines represent sections where refrigerant does
not flow. FIG. 5 is a P-h diagram in the cooling operation of the
air-conditioning apparatus 100 according to Embodiment 1 of the
present invention. In FIG. 5, point (a) to point (d) represent the
states of refrigerant at points denoted by the same characters in
FIG. 4.
[0058] When an operation starts, the compressor 11 sucks
low-temperature low-pressure gas refrigerant through the suction
pipe 23, compresses the refrigerant, and discharges
high-temperature high-pressure gas refrigerant. In this refrigerant
compression process of the compressor 11, refrigerant is compressed
with heat to a degree corresponding to an adiabatic efficiency of
the compressor 11, as compared to adiabatic compression represented
by an isentrope, as indicated by a curve from point (a) to point
(b) in FIG. 5. High-temperature high-pressure gas refrigerant
discharged from the compressor 11 passes through the
cooling/heating switching device 12 to be branched into two
refrigerant parts. One of the two refrigerant parts passes through
the first solenoid valve 16a and flows into the outdoor heat
exchanger 13a from the second connection pipe 25a. The other passes
through the first solenoid valve 16b and flows into the outdoor
heat exchanger 13b from the second connection pipe 25b.
[0059] The refrigerant that has flowed into the outdoor heat
exchangers 13a and 13b is cooled while heating outdoor air through
heat exchange with the outdoor air and becomes a medium-temperature
high-pressure liquid refrigerant. In consideration of a pressure
loss in the outdoor heat exchangers 13, a refrigerant change in the
outdoor heat exchangers 13a and 13b is represented a slightly
tilted approximately horizontal line indicated by a line from point
(b) to point (c) in FIG. 5. Here, heat exchange is performed in
both of the outdoor heat exchangers 13a and 13b. Alternatively, in
a case where the operation capacities of the indoor units 30a and
30b are small, for example, the first solenoid valve 16b may be
closed so that no refrigerant flows into the outdoor heat exchanger
13b. By preventing refrigerant from flowing, the heat transfer area
of the outdoor heat exchangers 13 decreases consequently, thereby
performing an operation in stable cycles.
[0060] The medium-temperature high-pressure liquid refrigerants
that have flowed out from the outdoor heat exchangers 13a and 13b
respectively flow into the first connection pipes 24a and 24b, pass
through the second flow rate control devices 15a and 15b in fully
opened states, and then are combined. The combined refrigerant
flows out of the outdoor unit 10. Then, the refrigerant passes
through the second extension pipes 50, 51a, and 51b and flows into
the indoor units 30a and 30b. The refrigerant then passes through
first flow rate control devices 32a and 32b. While passing through
the first flow rate control devices 32a and 32b, the refrigerant is
expanded and has its pressure reduced and becomes refrigerant in a
low-temperature low-pressure two-phase gas-liquid state. The change
of refrigerant in the first flow rate control devices 32a and 32b
is performed under a constant enthalpy. The refrigerant change at
this time is represented by a vertical line from point (c) to point
(d) in FIG. 5.
[0061] The refrigerant in the low-temperature low-pressure
two-phase gas-liquid state that has flowed out of the first flow
rate control devices 32a and 32b flows into indoor heat exchangers
31a and 31b. The refrigerant that has flowed into the indoor heat
exchangers 31a and 31b is heated while cooling indoor air through
heat exchange with the indoor air, and becomes low-temperature
low-pressure gas refrigerant. Here, the control device 60 controls
the opening degrees of the first flow rate control devices 32a and
32b in such a manner that the superheat (degree of superheat) of
the low-temperature low-pressure gas refrigerant from the indoor
heat exchangers 31a and 31b is about 2 K to 5 K. In consideration
of a pressure loss, the change of refrigerant in the indoor heat
exchangers 31a and 31b is represented by a slightly tilted
approximately horizontal line indicated by a line from point (e) to
point (a) in FIG. 5.
[0062] The low-temperature low-pressure gas refrigerant that has
flowed out of the indoor heat exchangers 31a and 31b flows out of
the indoor units 30a and 30b. The refrigerant then passes through
the first extension pipes 41a, 41b, and 40 and flows into the
outdoor unit 10. Thereafter, the refrigerant passes through the
cooling/heating switching device 12 and the accumulator 14 and is
sucked into the compressor 11 through the suction pipe 23.
[Heating Normal Operation]
[0063] FIG. 6 is a view showing a flow of refrigerant in a heating
normal operation of the air-conditioning apparatus 100 according to
Embodiment 1 of the present invention. In FIG. 6, bold lines
represent sections where refrigerant flows in the heating normal
operation, and thin lines represent sections where refrigerant does
not flow. FIG. 7 is a P-h diagram in the heating normal operation
of the air-conditioning apparatus 100 according to Embodiment 1 of
the present invention. In FIG. 7, point (a) to point (e) represent
the states of refrigerant at points denoted by the same characters
in FIG. 6.
[0064] When an operation starts, the compressor 11 sucks
low-temperature low-pressure gas refrigerant through the suction
pipe 23, compresses the refrigerant, and discharges
high-temperature high-pressure gas refrigerant. The refrigerant
compression process of the compressor 11 is represented by a curve
from point (a) to point (b) in FIG. 7.
[0065] The high-temperature high-pressure gas refrigerant
discharged from the compressor 11 passes through the
cooling/heating switching device 12 and then flows out of the
outdoor unit 10. The high-temperature high-pressure gas refrigerant
that has flowed out of the outdoor unit 10 flows into the indoor
units 30a and 30b through the first extension pipes 40, 41a, and
41b. The refrigerant then flows into the indoor heat exchangers 31a
and 31b. The refrigerant that has flowed into the indoor heat
exchangers 31a and 31b is cooled while heating indoor air through
heat exchange with the indoor air, and becomes medium-temperature
high-pressure liquid refrigerant. The change of refrigerant in the
indoor heat exchangers 31a and 31b is represented by a slightly
tilted approximately horizontal line from point (b) to point (c) in
FIG. 7.
[0066] The medium-temperature high-pressure liquid refrigerant that
has flowed out of the indoor heat exchangers 31a and 31b passes
through the first flow rate control devices 32a and 32b. While
passing through the first flow rate control devices 32a and 32b,
the refrigerant is expanded and has its pressure reduced and
becomes refrigerant in a medium-pressure two-phase gas-liquid
state. The change of refrigerant at this time is represented by a
vertical line from point (c) to point (d) in FIG. 7. The control
device 60 controls the opening degrees of the first flow rate
control devices 32a and 32b in such a manner that the subcooling
(degree of subcooling) of the medium-temperature high-pressure
liquid refrigerant is about 5K to 20K. The refrigerant in the
medium-pressure two-phase gas-liquid state that has flowed out of
the first flow rate control devices 32a and 32b flows out of the
indoor units 30a and 30b.
[0067] The refrigerant that has flowed out of the indoor units 30a
and 30b flows into the outdoor unit 10 through the second extension
pipes 51a, 51b, and 50. The refrigerant that has flowed into the
outdoor unit 10 flows into the first connection pipes 24a and 24b.
The refrigerant that has flowed into the first connection pipes 24a
and 24b passes through the second flow rate control devices 15a and
15b. While passing through the second flow rate control devices 15a
and 15b, the refrigerant is expanded and has its pressure reduced
and becomes a low-pressure two-phase gas-liquid state. The change
of refrigerant at this time is represented by a curve from point
(d) to point (e) in FIG. 7. The control device 60 controls the
opening degrees of the second flow rate control devices 15a and 15b
in such a manner that the opening degrees are fixed at a constant
opening degree (e.g., in a fully open state) or an
intermediate-pressure saturation temperature of the second
extension pipe 50, for example, is about 0 to 20 degrees C.
[0068] The refrigerant that has passed through the second flow rate
control devices 15a and 15b flows into the outdoor heat exchangers
13a and 13b. The refrigerant that has flowed into the outdoor heat
exchangers 13a and 13b is heated while cooling outdoor air through
heat exchange with the outdoor air and becomes low-temperature
low-pressure gas refrigerant. The change of refrigerant in the
outdoor heat exchangers 13a and 13b is represented by a slightly
tilted approximately horizontal line from point (e) to point (a) in
FIG. 7.
[0069] The low-temperature low-pressure gas refrigerants that have
flowed out of the outdoor heat exchangers 13a and 13b respectively
flow into the second connection pipes 25a and 25b, pass through the
first solenoid valves 16a and 16b, and then are combined. The
combined refrigerant passes through the cooling/heating switching
device 12 and the accumulator 14 and is sucked into the compressor
11 through the suction pipe 23.
[Heating Defrosting Operation (Continuous Heating Operation)]
[0070] A heating defrosting operation is performed when the control
device 60 determines that frost is accumulated on the outdoor heat
exchangers 13 in the heating normal operation. A plurality of
methods can be employed to determine the presence of frost
accumulation on the outdoor heat exchangers 13. As one example,
frost is determined to be accumulated if a saturation temperature
obtained by conversion from a suction pressure of the compressor 11
is determined to decrease significantly from a predetermined
outdoor-air temperature. As another example, frost is determined to
be accumulated if a temperature difference between an outdoor-air
temperature and an evaporating temperature in the outdoor heat
exchangers 13 is determined to be greater than or equal to a
predetermined difference for a predetermined period or longer.
[0071] In the configuration of the air-conditioning apparatus 100
according to Embodiment 1, while the outdoor heat exchanger 13b is
being defrosted in the heating defrosting operation, the outdoor
heat exchanger 13a serves as an evaporator so as to continue
heating. In contrast, while the outdoor heat exchanger 13a is being
defrosted, the outdoor heat exchanger 13b serves as an evaporator
so as to continue heating. Between the case of defrosting the
outdoor heat exchanger 13a and the case of defrosting the outdoor
heat exchanger 13b, the open/close states of the first solenoid
valve 16, the second solenoid valve 17, and the third solenoid
valve 19 are reversed and the flow of refrigerant in the outdoor
heat exchangers 13 are different, but the other part of the
operation is the same. Thus, the following description is directed
to the case where the outdoor heat exchanger 13b is defrosted and
the outdoor heat exchanger 13a serves as an evaporator so as to
continue heating in the heating defrosting operation. The same
holds for the subsequent embodiments.
[0072] FIG. 8 is a view showing a flow of refrigerant in a heating
defrosting operation of the air-conditioning apparatus 100
according to Embodiment 1 of the present invention. In FIG. 8, bold
lines represent sections where refrigerant flows in defrosting of
the outdoor heat exchanger 13b, and thin lines represent sections
where refrigerant does not flow. FIG. 9 is a P-h diagram in the
heating defrosting operation of the air-conditioning apparatus 100
according to Embodiment 1 of the present invention. In FIG. 9,
point (a) to point (i) represent the states of refrigerant at
points denoted by the same characters in FIG. 8.
[0073] The control device 60 determines which one of the outdoor
heat exchangers 13 is be defrosted. If it is determined that the
outdoor heat exchanger 13b is to be defrosted, the first solenoid
valve 16b corresponding to the outdoor heat exchanger 13b is
closed. The control device 60 opens the second solenoid valve 17b
and the third solenoid valve 19b and adjusts the reducing device 18
and the reducing device 20 to predetermined opening degrees.
[0074] In this manner, a refrigerant path (first refrigerant path)
passing through the compressor 11, the reducing device 18, the
second solenoid valve 17b, the outdoor heat exchanger 13b, the
second flow rate control device 15b, and the second flow rate
control device 15a in this order is formed. A refrigerant path
(medium-pressure defrosting circuit, second refrigerant path)
serving as an injection part and passing through the compressor 11,
the reducing device 18, the second solenoid valve 17b, the outdoor
heat exchanger 13b, the third solenoid valve 19b, the reducing
device 20, and the compressor 11 in this order is also formed.
Then, a heating defrosting operation starts.
[0075] When the heating defrosting operation starts, part of
high-temperature high-pressure gas refrigerant discharged from the
compressor 11 flows into the first defrosting pipe 26 and has its
pressure reduced to a medium pressure in the reducing device 18.
The change of refrigerant at this time is represented by a line
from point (b) to point (f) in FIG. 9.
[0076] The refrigerant whose pressure has been reduced to the
medium pressure represented by point (f) in FIG. 9 passes through
the second solenoid valve 17b and the second connection pipe 25b,
and flows into the outdoor heat exchanger 13b. The refrigerant that
has flowed into the outdoor heat exchanger 13b is cooled through
heat exchange with frost accumulated on the outdoor heat exchanger
13b. In this manner, high-temperature high-pressure gas refrigerant
discharged from the compressor 11 flows into the outdoor heat
exchanger 13b so that frost accumulated on the outdoor heat
exchanger 13b can be melted. The change of refrigerant at this time
is represented as a change from point (f) to point (g) in FIG. 9.
Here, refrigerant for defrosting has a saturation temperature
higher than a frost temperature (0 degrees C.) and lower than or
equal to 10 degrees C.
[0077] Part of refrigerant after defrosting passes through the
second flow rate control device 15b. The refrigerant that has
passed through the second flow rate control device 15b is combined
with refrigerant that has flowed into the outdoor unit 10 from the
indoor unit 30 through the second extension pipes 51a, 51 b, and 50
(point (h)). The combined refrigerant flows into the outdoor heat
exchanger 13a through the second flow rate control device 15a and
the first connection pipe 24a. The refrigerant that has flowed into
the outdoor heat exchanger 13a is heated while cooling outdoor air
through heat exchange with the outdoor air and becomes
low-temperature low-pressure gas refrigerant. On the other hand,
the other part of refrigerant that did not pass through the second
flow rate control device 15b passes through the third solenoid
valve 19b by way of the medium-pressure defrosting circuit
described above. Then, the refrigerant has its pressure reduced to
an injection pressure (point (i)) in the reducing device 20 and is
injected into the compressor 11.
[0078] Then, a reason for setting the saturation temperature of
refrigerant for refrigerant higher than 0 degrees C. and lower than
or equal to 10 degrees C. will be described.
[0079] FIGS. 10 to 14 are graphs in which the pressure (converted
into a saturated liquid temperature in each graph) of refrigerant
in the outdoor heat exchanger 13 to be defrosted with a fixed
defrosting capacity. In this example, R410A refrigerant is used as
refrigerant in the refrigerant circuit. FIG. 10 shows a change in
heating capacity with respect to a pressure change of refrigerant.
FIG. 11 shows a change of an enthalpy difference of refrigerant
between before inflow and after outflow of refrigerant into/from
the outdoor heat exchanger 13 to be defrosted with respect to a
pressure change of refrigerant. FIG. 12 shows a change of flow rate
of refrigerant necessary for defrosting with respect to a pressure
change of refrigerant. FIG. 13 shows a change of refrigerant amount
in the accumulator 14 and the outdoor heat exchanger 13 with
respect to a pressure change of refrigerant. FIG. 14 shows a change
of subcooling SC at a refrigerant outlet of the outdoor heat
exchanger 13 to be defrosted with respect to a pressure change of
refrigerant.
[0080] FIG. 10 shows that the heating capacity of the outdoor heat
exchanger 13 to be defrosted is high when the saturated liquid
temperature of refrigerant is higher than 0 degrees C. and is lower
than or equal to 10 degrees C., and is low otherwise. First, a
reason for the decrease of the heating capacity when the saturated
liquid temperature is lower than or equal to 0 degrees C. will be
described. To melt frost, the temperature of refrigerant needs to
be higher than 0 degrees C. As shown in FIG. 10, when the saturated
liquid temperature is reduced to 0 degrees C. or less in order to
melt frost, the location of point (g) in FIG. 9 becomes higher than
the saturation gas enthalpy. Thus, condensation latent heat of
refrigerant cannot be used, and the enthalpy difference between
before inflow and after outflow of refrigerant into/from the
outdoor heat exchanger 13 to be defrosted decreases (FIG. 11). At
this time, to show a defrosting capacity substantially equal to
that of refrigerant whose saturation temperature is higher than 0
degrees C. and lower than or equal to 10 degrees C., refrigerant in
an amount about three to four times as much as refrigerant having a
saturation temperature higher than 0 degrees C. and lower than or
equal to 10 degrees C. needs to flow into the outdoor heat
exchanger 13 to be defrosted. Thus, the amount of refrigerant that
can be supplied to the indoor unit 30 for heating decreases,
resulting in a decrease of the heating capacity. Accordingly, when
the saturated liquid temperature is 0 degrees C. or less, the
heating capacity decreases in a manner similar to the low-pressure
defrosting described in Patent Literature 1. In view of this, the
pressure of the outdoor heat exchanger 13 to be defrosted needs to
be higher than 0 degrees C. in terms of saturated liquid
temperature.
[0081] On the other hand, as the pressure of the outdoor heat
exchanger 13 to be defrosted increases, the subcooling SC at the
refrigerant outlet of the outdoor heat exchanger 13 to be defrosted
increases, as shown in FIG. 14. Accordingly, the amount of liquid
refrigerant increases, and the refrigerant density increases. In a
typical multi-air-conditioning apparatus for buildings, the amount
of necessary refrigerant is larger in cooling than in heating.
Thus, surplus refrigerant is usually present in a reservoir such as
the accumulator 14 in a heating operation. However, when the amount
of refrigerant necessary for the outdoor heat exchanger 13 to be
defrosted increases with the increase in pressure as shown in FIG.
13, the amount of refrigerant accumulated in the accumulator 14
decreases so that the accumulator 14 becomes empty at a saturation
temperature of about 10 degrees C. When the accumulator 14 becomes
empty of surplus refrigerant, shortage of refrigerant occurs in the
refrigeration cycle so that the suction density of the compressor
11 decreases, for example, causing a decrease in the heating
capacity. Although the upper limit of the saturation temperature
can be increased by overcharging with refrigerant, the reliability
of the air-conditioning apparatus might decrease because of, for
example, overflow of liquid from the accumulator 14 in other
operations. To prevent this, it is preferable to charge with an
appropriate amount of refrigerant. There is another problem that an
increase in the saturation temperature causes a temperature
variation in the temperature difference between refrigerant in the
outdoor heat exchanger 13 and frost, and thus, there arise a place
where frost is readily melted and a place where frost is not
readily melted.
[0082] For the foregoing reasons, the pressure of the outdoor heat
exchanger 13 to be defrosted is preferably higher than 0 degrees C.
and lower than or equal to 10 degrees C. in terms of saturation
temperature. To reduce variations in melting by suppressing
refrigerant movement during defrosting while making the most of the
medium-pressure defrosting using latent heat, an optimum target
value is obtained in a case where the subcooling SC at the outlet
of the outdoor heat exchanger 13 to be defrosted is 0 (zero) K. In
consideration of accuracies of, for example, a thermometer for
detecting subcooling and a pressure gauge, the pressure of the
outdoor heat exchanger 13 to be defrosted is preferably higher than
0 degrees C. and lower than or equal to 6 degrees C. in terms of
saturation temperature in order to set the subcooling SC in the
range from about 0 K to about 5K.
[0083] Then, an example of operations of the reducing devices 18
and 20 and the second flow rate control devices 15a and 15b during
a heating defrosting operation will be described. During the
heating defrosting operation, the control device 60 controls the
opening degree of the second flow rate control device 15b such that
the pressure of the outdoor heat exchanger 13b to be defrosted is
higher than 0 degrees C. and lower than or equal to 10 degrees C.
in terms of saturation temperature. On the other hand, regarding
the opening degree, the second flow rate control device 15a is
fully opened in order to enhance controllability by providing a
differential pressure between before inflow and after outflow of
refrigerant into/from the second flow rate control device 15b. The
opening degree of the reducing device 18 is fixed in accordance
with a predetermined necessary defrosting flow rate. This is
because the difference between the discharge pressure of the
compressor 11 and the pressure of the outdoor heat exchanger 13b to
be defrosted does not significantly change during the heating
defrosting operation. In addition, the reducing device 20 is
controlled to have such an opening degree that prevents liquid
compression of refrigerant in the compressor 11 in order to
maintain reliability. The opening degree of the reducing device 20
is controlled to such a degree that refrigerant can be injected
into the compressor 11 until the discharge superheat reaches about
10K to 20K, for example, in order to control, for example, the
discharge temperature and discharge superheat of the compressor 11
and, thereby, increase the flow rate of refrigerant flowing into
the indoor heat exchanger 31 serving as a condenser. Here, heat
released from refrigerant for defrosting does not only move to
frost accumulated on the outdoor heat exchanger 13b but also
partially moves to the outdoor air in some cases. Thus, the control
device 60 may control the reducing device 18 and the second flow
rate control device 15b in such a manner that the flow rate
increases as the outdoor-air temperature decreases. In this manner,
the quantity of heat to be applied to frost is made constant, and
thereby, the time for defrosting can be made constant, irrespective
of the outdoor-air temperature.
[0084] The control device 60 may change the threshold value and the
period of normal operation, for example, for use in determining the
presence of frost accumulation, in accordance with the outdoor-air
temperature. For example, the operating time is reduced so that the
frost accumulation amount at the start of defrosting decreases as
the outdoor-air temperature decreases in order to uniformize the
quantity of heat applied to defrosting from refrigerant during the
heating defrosting operation. In this manner, the resistance of the
reducing device 18 can be made uniform. In addition, a reasonable
capillary tube can be used. The control device 60 may set a
threshold value to the outdoor-air temperature. For example, in a
case where the outdoor-air temperature is determined to be a
threshold temperature or higher (e.g., in a case where the
outdoor-air temperature is -5 degrees C. or -10 degrees C.), the
heating defrosting operation is performed, whereas in a case where
the outdoor-air temperature is determined to be lower than the
threshold temperature, heating of the indoor unit 30 is stopped and
all the outdoor heat exchangers are defrosted. Specifically, in a
case where the outdoor-air temperature is lower than or equal to 0
degrees C., such as -5 degrees C. or -10 degrees C., the absolute
humidity of outdoor air is originally low and the frost
accumulation amount is small. Thus, the period of normal operation
until the frost accumulation amount becomes constant increases.
Accordingly, even when heating of the indoor unit 30 is stopped and
defrosting of all the outdoor heat exchangers 13 (full-surface
defrosting) is performed, the proportion of a period in which
heating of the indoor unit 30 is stopped is low. In the case of the
heating defrosting operation, in consideration of heat transfer
from the outdoor heat exchanger 13 to be defrosted to the outdoor
air, a higher efficiency is obtained by performing full-surface
defrosting with a heating operation stopped, for example, in some
cases. In view of this, a heating-stop defrosting operation mode in
which full-surface defrosting is performed may be selected, in
addition to the heating-and-defrosting operation mode. For example,
defrosting can be efficiently performed by selecting an operation
mode for defrosting based on the outdoor-air temperature.
[0085] In a case where the outdoor heat exchangers 13a and 13b are
integrally formed and outdoor air is conveyed to the outdoor heat
exchanger 13 to be defrosted by the outdoor fan 21, fan power may
be changed to decrease as the outdoor-air temperature decreases.
Thus, the amount of heat transferred from the outdoor heat
exchanger 13 to be defrosted can be reduced in the heating
defrosting operation.
[Control Flow]
[0086] FIG. 15 is a flowchart showing control of the control device
60 in the air-conditioning apparatus 100 according to Embodiment 1
of the present invention. Referring to FIG. 15, a control process
performed by the control device 60 in this embodiment will be more
specifically described. Here, the case of performing only a heating
defrosting operation will be described with reference to FIG.
15.
[0087] When the air-conditioning apparatus 100 starts an operation
(S1), it is determined whether or not the indoor units 30a and 30b
perform heating (whether or not the operation mode is heating)
(S2). If it is determined that the operation mode is cooling,
control of a normal cooling operation is performed (S3).
[0088] On the other hand, if it is determined that the operation
mode is heating, control of a normal heating operation is performed
(S4). In the normal heating operation, in consideration of
degradation of heat transmission performance of the outdoor heat
exchanger 13 caused by decrease in, for example, heat transmission
and the airflow rate due to frost accumulation, for example, it is
determined whether or not conditions for starting a heating
defrosting operation (whether or not frost is accumulated), based
on Equation (1) (S5). In Equation (1), x1 is about 5 K to 20 K. If
it is determined whether frost accumulation occurs or not by using
a temperature sensor, a pressure sensor, and a sensor for measuring
a frost accumulation amount, for example, the determination does
not depend on a suction pressure with respect to conditions for
starting defrosting.
(Saturation temperature of suction pressure)<(outdoor-air
temperature)-x1 (1)
[0089] For example, if it is determined that conditions for
starting the heating defrosting operation are satisfied based on
Equation (1), for example, a heating defrosting operation of
defrosting the outdoor heat exchanger 13 starts. Here, control in
the case of defrosting the outdoor heat exchanger 13b disposed at a
lower stage and the outdoor heat exchanger 13a disposed at an upper
stage in the outdoor heat exchangers 13 shown in FIG. 2 in this
order will be described as an example. Thus, defrosting
(medium-pressure defrosting) is first performed on the outdoor heat
exchanger 13b (S6). The order of defrosting may be reversed.
[0090] As described above, the valves in a heating normal operation
before a heating defrosting operation are in the states indicated
in the level of "heating normal operation" in FIG. 3. From these
states, the valves are changed to the states indicated in the level
of "13a: Evaporator 13b: Defrosting" in "heating defrosting
operation" in FIG. 3, and a heating defrosting operation is
performed (S7).
TABLE-US-00001 (a) First solenoid valve 16b OFF (b) Second solenoid
valve 17b ON (c) Third solenoid valve 19b ON (d) Reducing device 18
Open to a predetermined opening degree (e) Reducing device 20 Open
to a predetermined opening degree (f) Second flow rate control
Fully open device 15a (g) Second flow rate control Control starts
device 15b (h) Reducing device 20 Control starts
[0091] It is determined whether defrosting end conditions are
satisfied or not depending on melting of frost on the outdoor heat
exchanger 13b to be defrosted (S8). If it is determined that the
defrosting end conditions are not satisfied, a heating defrosting
operation is performed in such a manner that the outdoor heat
exchanger 13b is defrosted and the outdoor heat exchanger 13a
serves as an evaporator. Specifically, when the heating defrosting
operation continues so that frost accumulated on the outdoor heat
exchanger 13b starts being melted, the refrigerant temperature in
the first connection pipe 24b increases. Thus, for the defrosting
end conditions, the defrosting end conditions are determined to be
satisfied if a temperature sensor attached to the first connection
pipe 24b exceeds a threshold value as shown in Equation (2) below,
for example. Here, x2 is set at 3 to 10 degrees C., for
example.
(Refrigerant temperature of first connection pipe 24)>x2 (2)
[0092] If Equation (2) is satisfied and the defrosting end
conditions are determined to be satisfied, defrosting of the
outdoor heat exchanger 13b is finished (S9). At this time, the
states of the valves are changed as follows:
TABLE-US-00002 (a) Second solenoid valve 17b OFF (b) Third solenoid
valve 19b OFF (c) First solenoid valve 16b ON (d) Second flow rate
control Normal intermediate-pressure device 15a, 15b control
[0093] In addition, the valves are changed to the states indicated
in the levels of "13a: Defrosting 13b: Evaporator" in "heating
defrosting operation" in FIG. 3, and a heating defrosting operation
in which the outdoor heat exchanger 13a is defrosted starts (S10).
Although steps S10 to S13 are performed on the values indicated by
reference numerals different from those in steps S6 to S9, steps
S10 to S13 themselves are the same as steps S6 to S9.
[0094] When defrosting of both the lower-stage outdoor heat
exchanger 13b and the upper-stage outdoor heat exchanger 13a is
completed as described above and the heating defrosting operation
indicated by S6 to S13 is finished, the process returns to S4, and
a heating normal operation is performed.
[0095] Here, in a heating defrosting operation, the outdoor heat
exchangers 13 are sequentially defrosted each at least once.
Specifically, when defrosting of the last outdoor heat exchanger 13
is finished, a temperature sensor disposed in the refrigerant
circuit, for example, determines that frost is accumulated on the
initially defrosted outdoor heat exchanger 13 to degrade heat
transmission performance, the initially defrosted outdoor heat
exchanger 13 may be defrosted at the second time for a short
time.
[0096] As described above, in the air-conditioning apparatus 100
according to Embodiment 1, a heating defrosting operation is
performed in such a manner that defrosting is performed while
refrigerant is sent toward the indoor unit 30. Thus, the room can
be continuously heated. At this time, part of or the whole of
refrigerant that has flowed out of the outdoor heat exchanger 13
that is being defrosted can be injected into the compressor 11 by
adjusting the opening degree of at least one (mainly the reducing
device 20) of the reducing device 20 or the second flow rate
control device 15. Thus, the amount of refrigerant supplied to the
indoor unit 30 is increased so that heating capacity can be
enhanced. In this operation, since each of the outdoor heat
exchangers 13 is defrosted at least once, the efficiency in a
normal heating operation can be increased.
[0097] In addition, part of refrigerant that has flowed out of the
outdoor heat exchanger 13 being defrosted can be caused to flow
into a main refrigerant circuit upstream of the outdoor heat
exchanger 13 serving as an evaporator, by adjusting the opening
degree of at least one (mainly the second flow rate control device
15) of the reducing device 20 and the second flow rate control
device 15. Thus, the defrosting efficiency can be enhanced, the
amount of refrigerant flowing into the outdoor heat exchanger 13
serving as an evaporator increases, and the amount of heat
absorption from the outdoor air increases. In addition, a decrease
in the suction pressure of the compressor 11 can be suppressed.
[0098] Furthermore, the reducing device 20 is controlled to an
opening degree at which refrigerant is injected in such a manner
that the discharge superheat of refrigerant discharged from the
compressor 11 is about 10K to 20K. Thus, the amount of refrigerant
flowing into the indoor heat exchanger 31 serving as a condenser
increases while the reliability is maintained so as to prevent
refrigerant from liquid compression in the compressor 11, thereby
enhancing the heating capacity.
[0099] In the air-conditioning apparatus 100 of this embodiment,
part of high-temperature high-pressure gas refrigerant branched off
from the discharge pipe 22 is subjected to pressure reduction to a
pressure (medium pressure) higher than 0 degrees C. and lower than
or equal to 10 degrees C., in terms of saturation temperature, as
compared to the temperature of frost, and the resulting refrigerant
flows into the outdoor heat exchanger 13 to be defrosted. Thus,
defrosting can be performed while utilizing condensation latent
heat of refrigerant.
[0100] In the air-conditioning apparatus 100 of this embodiment,
the saturation temperature is higher than 0 degrees C. and lower
than or equal to 10 degrees C. so as to reduce the temperature
difference between the saturation temperature and the frost
temperature. Thus, the subcooling (degree of subcooling) of
refrigerant at the outlet of the outdoor heat exchanger 13 to be
defrosted is as small as about 5 K. Thus, a small amount of
refrigerant is necessary for defrosting, and a shortage of
refrigerant circulating in the main refrigerant circuit can be
avoided. In addition, an area of two-phase gas-liquid is increased
for refrigerant in the heat transfer tube of the outdoor heat
exchanger 13 to be defrosted, an area where the temperature
difference between the saturation temperature and the frost
temperature is uniform, and the amount of defrosting in the entire
heat exchangers can be uniformized.
[0101] In the air-conditioning apparatus 100 of this embodiment,
refrigerant that has flowed out of the outdoor heat exchanger 13 to
be defrosted flows into the other outdoor heat exchanger 13 serving
as an evaporator. Thus, the evaporative capacity in the
refrigeration cycle is maintained, and a decrease in the suction
pressure can be suppressed. In addition, liquid back to the
compressor 11 can be prevented. Furthermore, the flow rate control
of the reducing device 18 can change the defrosting capacity. Thus,
the increase in the flow rate of the reducing device 18 as the
outdoor-air temperature decreases, can uniformize the time for
defrosting.
[0102] In the air-conditioning apparatus 100 of this embodiment,
the time necessary for defrosting can be uniformized by changing a
criterion for determining whether to perform a heating defrosting
operation or not based on the outdoor-air temperature, for example.
In addition, since the heating defrosting operation and the
heating-stop defrosting operation can be selectively performed
based on the outdoor-air temperature, efficient defrosting can be
selectively performed. Furthermore, since output power of the
outdoor fan 21 is changed based on the outdoor-air temperature, the
amount of heat transferred to the outdoor air from refrigerant for
defrosting can be reduced.
Embodiment 2
[0103] FIG. 16 illustrates a configuration of an air-conditioning
apparatus 101 according to Embodiment 2 of the present invention.
In FIG. 16, devices designated by the same reference characters,
for example, perform similar operations, for example, to those
described in Embodiment 1. Part of the configuration of the
air-conditioning apparatus 101 different from that of the
air-conditioning apparatus 100 of the Embodiment 1 will be
hereinafter mainly described.
[0104] The air-conditioning apparatus 101 according to Embodiment 2
includes a third flow rate control device 15c and a
refrigerant-to-refrigerant heat exchanger 28 (hereinafter referred
to as a refrigerant-refrigerant heat exchanger 28) in addition to
the configuration of the air-conditioning apparatus 100 of
Embodiment 1. The third flow rate control device 15c is disposed in
a pipe connecting a first connection pipe 24a and a first
connection pipe 24b for bypassing. The third flow rate control
device 15c is constituted by, for example, a valve having a
variable opening degree, such as an electronically controlled
expansion valve. The third flow rate control device 15c of this
embodiment corresponds to a "third pressure adjustment device" of
the present invention. Thus, although the air-conditioning
apparatus 101 illustrated in FIG. 16 includes the second flow rate
control devices 15a and 15b, the second flow rate control devices
15a and 15b are not necessarily provided.
[0105] FIG. 17 is a table showing states of ON/OFF
(opening/closing) or opening degree adjustment of devices (valves)
having valves in operations of the air-conditioning apparatus 101
according to Embodiment 2 of the present invention. Operations of
the second flow rate control devices 15a and 15b and the third flow
rate control device 15c in the air-conditioning apparatus 101 of
this embodiment are different from those in Embodiment 1.
[0106] In a heating defrosting operation, the third flow rate
control device 15c causes refrigerant that has flowed from an
outdoor heat exchanger 13 to be defrosted to flow into a part
upstream of an outdoor heat exchanger 13 serving as an evaporator.
The third flow rate control device 15c is controlled by a control
device 60 in such a manner that a pressure of the outdoor heat
exchanger 13 to be defrosted is a medium pressure higher than 0
degrees C. and lower than or equal to 10 degrees C. On the other
hand, the second flow rate control device 15a or 15b, which
controls the pressure of the outdoor heat exchanger 13 to be
defrosted in Embodiment 1, is closed. The second flow rate control
device 15a or 15b, which is fully open in Embodiment 1, is
controlled to have an opening degree with which the saturation
temperature at an intermediate pressure of, for example, a second
extension pipe 50 is about 0 degrees C. to 20 degrees C.
[0107] FIG. 18 is a view showing a flow of refrigerant in a heating
defrosting operation of the air-conditioning apparatus 101
according to Embodiment 2 of the present invention. In FIG. 18,
bold lines represent sections where refrigerant flows in the
heating defrosting operation, and thin lines represent sections
where refrigerant does not flow. FIG. 19 is a P-h diagram in the
heating defrosting operation of the air-conditioning apparatus 101
according to Embodiment 2 of the present invention. In FIG. 19,
point (a) to point (i) represent the states of refrigerant at
points denoted by the same characters in FIG. 18.
[0108] If it is determined that defrosting for eliminating frost
accumulation is necessary in a heating normal operation, the
control device 60 closes a first solenoid valve 16b and a second
flow rate control device 15b corresponding to the outdoor heat
exchanger 13b to be defrosted. The control device 60 opens a second
solenoid valve 17b and a third solenoid valve 19b and sets the
opening degrees of the reducing device 18 and the reducing device
20 at predetermined opening degrees. The control device 60 sets the
opening degree of the third flow rate control device 15c at a
predetermined opening degree.
[0109] In this manner, a refrigerant path (first refrigerant path)
passing through a compressor 11, a reducing device 18, the second
solenoid valve 17b, the outdoor heat exchanger 13b, and the third
flow rate control device 15c in this order is formed. A refrigerant
path (medium-pressure defrosting circuit, second refrigerant path)
serving as an injection part and passing through the compressor 11,
the reducing device 18, the second solenoid valve 17b, the outdoor
heat exchanger 13b, the third solenoid valve 19b, the
refrigerant-refrigerant heat exchanger 28, the reducing device 20,
and the compressor 11 in this order is also formed. Then, a heating
defrosting operation starts.
[0110] When the heating defrosting operation starts, part of
high-temperature high-pressure gas refrigerant discharged from the
compressor 11 flows into a first defrosting pipe 26 and has its
pressure reduced to a medium pressure in the reducing device 18.
The change of refrigerant at this time is represented by a line
from point (b) to point (f) in FIG. 19.
[0111] The refrigerant whose pressure has been reduced to the
medium pressure represented by point (f) in FIG. 19 passes through
the second solenoid valve 17b and the second connection pipe 25b,
and flows into the outdoor heat exchanger 13b. The refrigerant that
has flowed into the outdoor heat exchanger 13b is cooled through
heat exchange with frost accumulated on the outdoor heat exchanger
13b. The change of refrigerant at this time is represented by a
change from point (f) to point (g) in FIG. 19. Here, refrigerant
for defrosting is at a saturation temperature higher than or equal
to frost temperature (0 degrees C.) and lower than or equal to 10
degrees C.
[0112] The refrigerant used for defrosting the outdoor heat
exchanger 13b is branched into to refrigerant parts. One of the two
refrigerant parts passes through the third flow rate control device
15c and flows into the main refrigerant circuit from the first
connection pipe 24a between the second flow rate control device 15a
and the outdoor heat exchanger 13a (point (e)). This refrigerant
flows into the outdoor heat exchanger 13a serving as an evaporator
and evaporates.
[0113] The other refrigerant part passes through the third solenoid
valve 19b, and exchanges heat, in the refrigerant-refrigerant heat
exchanger 28, with refrigerant for heating flowing at an
intermediate pressure at which a saturation temperature is higher
than that at a medium pressure represented by point (f). The
refrigerant heated by the heat exchange has its pressure reduced to
an injection pressure in the reducing device 20 (point (i)). At
this time, refrigerant for heating is cooled through heat exchange.
The change of refrigerant at this time is represented by a change
from point (d) to point (h) in FIG. 19.
[0114] As described above, in the air-conditioning apparatus 101
according to Embodiment 2, refrigerant that has passed through the
outdoor heat exchanger 13 to be defrosted flows under a low
pressure (corresponding to a suction pressure of the compressor
11). Thus, the control device 60 can perform control for the
intermediate pressure (point (d)) and control of the medium
pressure (point (f)), separately from each other. Since the
intermediate pressure may be higher than the medium pressure,
valves having small Cv values can be used as the second flow rate
control devices 15a and 15b.
[0115] In a case where the intermediate pressure is higher than the
medium pressure, refrigerant to be injected into the compressor 11
after having passed through the outdoor heat exchanger 13 to be
defrosted exchanges heat, in the refrigerant-refrigerant heat
exchanger 28, with refrigerant at the intermediate pressure that
has returned from the indoor units 30a and 30b to the outdoor unit
10 so that the refrigerant to be injected is heated and refrigerant
flowing in the main refrigerant circuit is cooled (subcooled).
Thus, in the outdoor heat exchanger 13 serving as an evaporator, an
enthalpy difference can be increased, and the amount of heat
absorption from the outdoor air can be increased, thereby enhancing
the heating capacity. In this aspect, in the air-conditioning
apparatus 100 of Embodiment 1 described above, since refrigerant
that has passed through the outdoor heat exchanger 13 to be
defrosted returns to the mainstream, the intermediate pressure
(pressure of the second extension pipe 50) needs to be made lower
than the medium pressure (pressure of refrigerant flowing into the
outdoor heat exchanger 13 to be defrosted).
Embodiment 3
[0116] FIG. 20 illustrates a configuration of an air-conditioning
apparatus 102 according to Embodiment 3 of the present invention.
In FIG. 20, devices designated by the same reference characters as
those in FIGS. 1 and 16, for example, perform similar operations,
for example, to those described in Embodiment 1 or 2. Thus, part of
the configuration of the air-conditioning apparatus 102 of this
embodiment different from that of the air-conditioning apparatus
101 of the Embodiment 2 will be hereinafter mainly described.
[0117] In addition to the configuration of the air-conditioning
apparatus 101 of Embodiment 2 described above, the air-conditioning
apparatus 102 according to Embodiment 3 includes a fourth flow rate
control device 29 for performing pressure adjustment in such a
manner that refrigerant flows from a pipe (pipe between a second
extension pipe 50 and second flow rate control devices 15a and 15b)
at an intermediate pressure in a main refrigerant circuit to a part
upstream of a refrigerant-refrigerant heat exchanger 28 of a second
defrosting pipe 27. In Embodiment 3, a third flow rate control
device 15c also corresponds to a "third reducing device" of the
present invention. The fourth flow rate control device 29
corresponds to a "fourth pressure adjustment device" of the present
invention.
[0118] In a manner similar to Embodiment 2, in a heating defrosting
operation of Embodiment 3, a refrigerant path (first refrigerant
path) passing through a compressor 11, a reducing device 18, a
second solenoid valve 17b, an outdoor heat exchanger 13b, and the
third flow rate control device 15c in this order is formed. A
refrigerant path (medium-pressure defrosting circuit, second
refrigerant path) serving as an injection part (port) and passing
through the compressor 11, the reducing device 18, the second
solenoid valve 17b, the outdoor heat exchanger 13b, the third
solenoid valve 19b, the refrigerant-refrigerant heat exchanger 28,
the reducing device 20, and the compressor 11 in this order is also
formed.
[0119] In the heating defrosting operation of Embodiment 3, the
third flow rate control device 15c and the fourth flow rate control
device 29 control a medium pressure. Specifically, in a case where
the third flow rate control device 15c is fully closed in
controlling the medium pressure with a low flow rate of refrigerant
for defrosting, the control device 60 adjusts the opening degree of
the fourth flow rate control device 29 so as to increase the medium
pressure.
[0120] Refrigerant that has passed through the third solenoid valve
19b exchanges heat with refrigerant for heating in the
refrigerant-refrigerant heat exchanger 28, in a manner similar to
Embodiment 2. Then, the degree of subcooling of refrigerant for
heating is increased, and the amount of heat absorption in the
outdoor heat exchanger 13 serving as an evaporator is increased,
thereby enhancing the heating capacity.
[0121] As described above, in the air-conditioning apparatus 102 of
Embodiment 3, the fourth flow rate control device 29 is made open
even in a case where the flow rate of refrigerant for defrosting is
low so that refrigerant at a medium pressure subjected to pressure
adjustment is caused to flow into the outdoor heat exchanger 13 to
be defrosted, and thereby, medium pressure control on the outdoor
heat exchanger 13 to be defrosted can be stably performed. In
addition, heat exchange in the refrigerant-refrigerant heat
exchanger 28 can increase the degree of subcooling of refrigerant
for heating. Thus, the amount of heat absorption from outdoor air
can be increased in the outdoor heat exchanger 13 serving as an
evaporator, thereby enhancing the heating capacity.
Embodiment 4
[0122] FIG. 21 illustrates a configuration of an air-conditioning
apparatus 103 according to Embodiment 4 of the present invention.
In FIG. 21, devices designated by the same reference characters as
those in FIG. 20, for example, perform similar operations, for
example, to those described in Embodiments 1 to 3. Part of the
configuration of the air-conditioning apparatus 103 of this
embodiment different from that of the air-conditioning apparatus
102 of the Embodiment 3 will be hereinafter mainly described.
[0123] In the air-conditioning apparatus 103 according to
Embodiment 4, one end of a first defrosting pipe 26 is connected to
first connection pipes 24a and 24b, instead of the configuration of
the air-conditioning apparatus 102 of Embodiment 3. In addition,
one end of the second defrosting pipe 27 is connected to second
connection pipes 25a and 25b.
[0124] The air-conditioning apparatus 102 of Embodiment 3 includes
the third flow rate control device for connecting the first
connection pipes 24a and 24b for bypassing. Alternatively, the
air-conditioning apparatus 103 of this embodiment includes a third
flow rate control device 15c and check valves 70a and 70b in such a
manner that refrigerant used for defrosting passes through the
second defrosting pipe 27 and a third defrosting pipe 71 and flows
toward a first connection pipe 24a or 24b. A third flow rate
control device 15c of an air-conditioning apparatus 104 and a
fourth flow rate control device 29 of the air-conditioning
apparatus 103 in Embodiment 4 respectively correspond to a "third
reducing device" and a "fourth reducing device" of the present
invention.
[0125] FIG. 22 illustrates a configuration of the air-conditioning
apparatus 104 according to Embodiment 4 of the present invention.
In the air-conditioning apparatus 104 illustrated in FIG. 22, the
third flow rate control device 15c and the check valves 70a and 70b
of the air-conditioning apparatus 103 are omitted.
[0126] In the configurations illustrated in FIGS. 21 and 22,
refrigerant in the outdoor heat exchangers 13 of the
air-conditioning apparatuses 103 and 104 of this embodiment flows
in a reverse direction to the flow of refrigerant in the
air-conditioning apparatuses 100 to 102 of Embodiments 1 to 3.
[0127] If it is determined that defrosting for eliminating frost
accumulation is necessary in a normal heating operation, the
control device 60 closes a first solenoid valve 16b corresponding
to an outdoor heat exchanger 13b to be defrosted and fully closes a
second flow rate control device 15b. The control device 60 opens a
second solenoid valve 17b and a third solenoid valve 19b and
adjusts the opening degree of the reducing device 18 to a
predetermined opening degree. The control device 60 opens the third
flow rate control device 15c in the air-conditioning apparatus 104
and opens the fourth flow rate control device 29 in the
air-conditioning apparatus 103.
[0128] In this manner, in the air-conditioning apparatus 103, a
refrigerant path (first refrigerant path) passing through a
compressor 11, the reducing device 18, the second solenoid valve
17b, an outdoor heat exchanger 13b, the third solenoid valve 19b,
the third flow rate control device 15c, and the first connection
pipe 24a in this order is formed. In the air-conditioning apparatus
104, a refrigerant path (first refrigerant path) passing through
the compressor 11, the reducing device 18, the second solenoid
valve 17b, the outdoor heat exchanger 13b, the third solenoid valve
19b, the fourth flow rate control device 29, the refrigerant heat
exchanger 28, the second flow rate control device 15a, and the
first connection pipe 24a in this order is also formed. As a second
path, a refrigerant path (medium-pressure defrosting circuit,
second refrigerant path) serving as an injection part (port) and
passing through the compressor 11, the reducing device 18, the
second solenoid valve 17b, the outdoor heat exchanger 13b, the
third solenoid valve 19b, the refrigerant heat exchanger 28, the
reducing device 20, and the compressor 11 in this order is formed.
Then, a heating defrosting operation starts.
[0129] In the heating defrosting operation, the control device 60
controls the opening degree of the third flow rate control device
15c or the fourth flow rate control device 29 in such a manner that
the pressure (medium pressure) of an outdoor heat exchanger 13b to
be defrosted is higher than 0 degrees C. and lower than or equal to
10 degrees C., in terms of saturation temperature. The reducing
device 20 has an opening degree at which refrigerant can be
injected into the compressor 11 until the discharge superheat
reaches about 10 K to 20 K, for example, so as to control the
discharge temperature and discharge superheat of the compressor 11,
for example.
[0130] As illustrated in FIG. 2, the first connection pipes 24a and
24b are connected to the heat transfer tubes 5a upstream of the
outdoor heat exchangers 13a and 13b in the air flow direction. The
heat transfer tubes 5a of the outdoor heat exchangers 13a and 13b
are arranged in a plurality of columns in the air flow direction
and refrigerant sequentially flows toward downstream rows. Thus,
refrigerant supplied to the outdoor heat exchanger 13b to be
defrosted flows from the heat transfer tubes 5a upstream in the air
flow direction to the downstream side, and parallel flows in which
the refrigerant flow direction coincides with the air flow
direction are obtained.
[0131] As described above, in the outdoor heat exchanger 13 to be
defrosted according to Embodiment 4, the refrigerant flow direction
can be made coincide with the air flow direction. The parallel flow
of refrigerant allows heat transferred to the air in defrosting to
be used for defrosting of frost on the downstream fins 5b. Thus,
the efficiency of defrosting can be increased.
Embodiment 5
[0132] In Embodiments 1 to 4, the outdoor heat exchangers 13 are
divided into two outdoor heat exchangers 13a and 13b. However, the
present invention is not limited to this example. In a
configuration including three or more outdoor heat exchangers,
application of the above-described inventive concept allows some of
the outdoor heat exchangers 13 to be defrosted with other outdoor
heat exchangers 13 continuing a heating operation.
[0133] In Embodiments 1 to 4, one outdoor heat exchanger is divided
into a plurality of outdoor heat exchangers 13. However, the
present invention is not limited to this example. In a
configuration including separate outdoor heat exchangers 13 that
are connected in parallel, application of the above-described
inventive concept allows part of the outdoor heat exchangers 13 to
be defrosted and another part of the outdoor heat exchangers 13 to
continue a heating operation.
REFERENCE SIGNS LIST
[0134] 5a heat transmission pipe, 5b fin, 10 outdoor unit, 11
compressor, 12 cooling/heating switching device, 13, 13a, 13b
outdoor heat exchanger, 14 accumulator, 15a, 15b second flow rate
control device, 15c third flow rate control device, 16, 16a, 16b
first solenoid valve, 17, 17a, 17b second solenoid valve, 18, 20
reducing device, 19, 19a, 19b third solenoid valve, 21 outdoor fan,
22 discharge pipe, 23 suction pipe, 24, 24a, 24b first connection
pipe, 25, 25a, 25b second connection pipe, first defrosting pipe,
27 second defrosting pipe, 28 refrigerant-refrigerant heat
exchanger, 29 fourth flow rate control device, 30, 30a, 30b indoor
unit, 31, 31a, 31b indoor heat exchanger, 32, 32a, 32b first flow
rate control device, 40, 41a, 41b first extension pipe, 50, 51a,
51b second extension pipe, 60 control device, 70a, 70b check valve,
71 third defrosting pipe, 100, 101, 102, 103, 104 air-conditioning
apparatus.
* * * * *